Leases (Details) $ in Thousands, ratio in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) unit	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months			$ 15,077
Operating Lease, Expense	$ 5,286	$ 4,200
Variable Lease, Cost	$ 571
Number of Properties Subject to Ground Leases | unit	22
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 11,811
Lessee, Operating Lease, Liability, Payments, Due Year Two	15,682
Lessee, Operating Lease, Liability, Payments, Due Year Three	14,537
Lessee, Operating Lease, Liability, Payments, Due Year Four	13,591
Lessee, Operating Lease, Liability, Payments, Due Year Five	13,102
Lessee, Operating Lease, Liability, Payments, Due after Year Five	604,282
Lessee, Operating Lease, Liability, Payments, Due	225,122
Lessor, Operating Lease, Payments to be Received, Two Years	713,553		693,848
Lessor, Operating Lease, Payments to be Received, Three Years	629,638		608,587
Lessor, Operating Lease, Payments to be Received, Four Years	537,753		516,369
Lessor, Operating Lease, Payments to be Received, Five Years	437,109		414,424
Lessor, Operating Lease, Payments to be Received, Thereafter	1,778,839		1,691,203
Lessor, Operating Lease, Payments to be Received	4,675,855		4,685,582
Operating cash flows from operating leases	$ 3,692
Last Ground Lease Expiration Date	2101
Last Office Lease Expiration Date	2029
Operating Leases, Future Minimum Payments, Due in Two Years			14,733
Operating Leases, Future Minimum Payments, Due in Three Years			13,893
Operating Leases, Future Minimum Payments, Due in Four Years			13,151
Operating Leases, Future Minimum Payments, Due in Five Years			12,558
Operating Leases, Future Minimum Payments, Due Thereafter			467,706
Operating Leases, Future Minimum Payments Due			537,118
Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year	$ 578,963		761,151
Lease Income	277,303
Fixed and in-substance fixed lease income	201,878
Variable lease income	62,835
Above/below market rent amortization	13,454
Amount of lease revenue determined to be uncollectible and charged to lease income	(864)
Fixed Lease Expense [Domain]
Operating Leased Assets [Line Items]
Operating Lease, Expense	4,715
Office Lease [Member]
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months			4,405
Operating Lease, Expense	1,042
Variable Lease, Cost	143
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	3,807
Lessee, Operating Lease, Liability, Payments, Due Year Two	4,976
Lessee, Operating Lease, Liability, Payments, Due Year Three	3,863
Lessee, Operating Lease, Liability, Payments, Due Year Four	2,893
Lessee, Operating Lease, Liability, Payments, Due Year Five	2,188
Lessee, Operating Lease, Liability, Payments, Due after Year Five	5,955
Lessee, Operating Lease, Liability, Payments, Due	$ 21,123
Operating Lease, Weighted Average Discount Rate, Percent	0.00%
Operating Lease, Weighted Average Remaining Lease Term	5 years 10 months 24 days
Operating Leases, Future Minimum Payments, Due in Two Years			4,294
Operating Leases, Future Minimum Payments, Due in Three Years			3,549
Operating Leases, Future Minimum Payments, Due in Four Years			2,893
Operating Leases, Future Minimum Payments, Due in Five Years			2,189
Operating Leases, Future Minimum Payments, Due Thereafter			5,944
Operating Leases, Future Minimum Payments Due			23,274
Ground Lease [Member]
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months			10,672
Operating Lease, Expense	$ 3,673
Variable Lease, Cost	428
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	8,004
Lessee, Operating Lease, Liability, Payments, Due Year Two	10,706
Lessee, Operating Lease, Liability, Payments, Due Year Three	10,674
Lessee, Operating Lease, Liability, Payments, Due Year Four	10,698
Lessee, Operating Lease, Liability, Payments, Due Year Five	10,914
Lessee, Operating Lease, Liability, Payments, Due after Year Five	598,327
Lessee, Operating Lease, Liability, Payments, Due	$ 203,999
Operating Lease, Weighted Average Discount Rate, Percent	0.00%
Operating Lease, Weighted Average Remaining Lease Term	49 years 10 months 24 days
Operating Leases, Future Minimum Payments, Due in Two Years			10,439
Operating Leases, Future Minimum Payments, Due in Three Years			10,344
Operating Leases, Future Minimum Payments, Due in Four Years			10,258
Operating Leases, Future Minimum Payments, Due in Five Years			10,369
Operating Leases, Future Minimum Payments, Due Thereafter			461,762
Operating Leases, Future Minimum Payments Due			$ 513,844
Undiscounted Amount [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Liability, Payments, Due	$ 673,005
Undiscounted Amount [Member] | Office Lease [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Liability, Payments, Due	23,682
Undiscounted Amount [Member] | Ground Lease [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Liability, Payments, Due	649,323
Discount Amount [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(447,883)
Discount Amount [Member] | Office Lease [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(2,559)
Discount Amount [Member] | Ground Lease [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	$ (445,324)